ALTERNATING MAGNETIC-FIELD SHIELDING OF YBCO TUBES IN STATIC-FIELD

The alternating magnetic field shielding efficiency of a YBCO tube was measured in a static field of up to 1 kG, bearing the possibility of its application as a field regulator in mind. The shielding efficiency is higher when the sample is field-cooled than when it is zero-field- cooled, as predicted by the critical state model. In the case of field cooling, the tube still shields about 25% of ac field of 1 kHz even i n 500 G dc field. Shielding efficiency monotonously increases with inc reasing frequency from 10 Hz to 1 kHz.